A study on time division duplex-based MAC protocol for WDM/Ethernet-passive optical networks

Abstract

In this thesis, we propose a new time division duplex (TDD)-based MAC protocol for WDM/Ethernet passive optical network (WE-PON) architecture over tree topology. On this architecture, single light source is reused at optical network termination (ONT) to modulate upstream signals for bidirectional communication. Once adopting such a technology, splitting ratio is significantly limited due to amplitude squeezing effect (ASE) at ONT. To address this problem, we propose a novel MAC protocol applying time division duplex (TDD) technology. As doing so, maximum 16 subscribers per wavelength can be serviced in the optical layer. But downstream bandwidth is inevitably taken away for upstream traffic in the network layer. To compensate downstream bandwidth used for up-traffic, we propose dynamic bandwidth sharing algorithms according to three cases: 1) adaptive threshold adjustment (ATA) and dynamic bandwidth algorithm (DBA) is provided in generating downstream frames in order to promptly response user request and 2) the up/down fair service algorithm based on ATA give both upstream and downstream traffic a equal right to be treated equally for user request and 3) finally QoS provisioning for downstream traffic supports guaranteed services for differentiated priority traffic under up/down fair service algorithm We used OPNET to simulate the network performance under various configurations of network parameters. The simulation results of MAC protocol with ATA_DBA in TDD-based WE-PON are close to ASE-based WE-PON with ATA_SBA in queueing delay, queue size, and link utilization. Also, upgraded ATA algorithm for up/down fair service ensures fairness in setting the threshold, higher bandwidth utilization compared to ASE-based WE-PON especially on environment of asynchronous traffic, and QoS for downstream traffic.